I remember being eight years old and asking my mother how to know if you are going to heaven or not. I wasn't raised in the church, but I heard people talk about going to heaven, so I was curious. She told me that if I'm good, I will go to heaven and be an angel. This comforted me at the time, but each time I did something wrong, I wondered if I would go to heaven. That fear lingered until years later when I read what the Bible had to say about it.
We often try to complicate how we can qualify for heaven, but the apostle John simplifies it for us. If you have the Son, you have life:
"And this is the testimony, that God gave us eternal life, and this life is in his Son. Whoever has the Son has life; whoever does not have the Son of God does not have life." (1 John 5:11-12, ESV)
Of course, we have to understand who the Son is, which he also explains. In verse 1 of chapter 5, he tells us that we must believe that Jesus is the Christ (the Messiah) and that he has been born of God. We also need to love the Father, or we won’t understand the Son.
Verse 5 says we must believe he is the Son of God.
Verses 6-8 bring the Spirit into the discussion, explaining that the Spirit is the one who testifies who Jesus is and what he has done for us. So not only do we have the testimony of flesh and blood people who have experienced Christ, but we have God’s own Spirit proclaiming the truth to us.